Pyrolytic carbon coatings have been used to protect particles of nuclear reactor fuel, i.e., fissile and/or fertile materials, such as uranium, plutonium and thorium in the form of suitable compounds thereof. Coatings of aluminum oxide and other ceramic oxides have also been proposed. Examples of nuclear fuel particles employing pyrolytic carbon coatings include U.S. Pat. No. 3,325,363, issued June 13, 1967; U.S. Pat. No. 3,298,921, issued Jan. 17, 1968, and U.S. Pat. No. 3,361,638, issued Jan. 2, 1968. It is also known to incorporate one or more layers of refractory carbide materials, such as silicon carbide or zirconium carbide, to produce nuclear fuel particles having still better fission product retention characteristics, as disclosed in U.S. Pat. No. 3,649,472, issued Mar. 14, 1972. So long as these fission product retentive coatings remain intact, contamination exterior of the particles by the heavy metal fuel material and/or substantial spread of fission products exterior of the coatings is prevented.
Such nuclear fuel particles are usually bonded together in some fashion to create what is termed in the art as a nuclear fuel compact, which is produced using a suitable binder and appropriate pressures. It has been found that fracture and/or cracking of the fission product retentive coatings often occurs during the formation of nuclear fuel compacts wherein these nuclear fuel particles are combined under high pressure with a binder material to produce a relatively dense "green" compact that is later subjected to high temperatures to produce the final nuclear fuel compact suitable for use in a nuclear reactor. It is also known to produce nuclear fuel compacts or nuclear fuel elements for a Pebble-Bed reactor or the like by blending such coated nuclear fuel particles with a carbonaceous thermosetting resin in a powder form and compressing the coated particle-resin mixture under pressures in excess of 20,000 psig to form "green" compacts, and sometimes these particles have been pre-treated with the resin. Nuclear fuel particles which can better tolerate such manufacturing processes are constantly being sought after.